I have a Coleman EB15B furnace / with heat pump coils installed. The furnace is 18 years old. This past month, the 16 x 20 inch fiter installed in it has collapsed into the unit. This is the same brand filter that I have been using all along have replaced almost monthly.. . I replaced it with a better brand of filter but had same results.. The Blend Air Solenoid is working properly (open when on) and nothing has changed or been altered that might impact return house air to the furnace. My thought was to support the filter on the end that is inserted into the furnace as it only sits on two supporting sheet metal side rails.. BUT something is causing the filters to colapse into the furnace.. The flow arrow on the filter is pointed down in the correct direction.. I am lost on this one as the heating and cooling functions are working fine.. just filter cave in.. IDEAS..SUGGESTIONS??